TKTS Booth

The new TKTS booth in Times Square is topped by a cascade of 27 ruby-red translucent structural glass steps, rising to a height of 16 feet 1 inch above the 47th Street sidewalk. It has become a focal meeting point for New Yorkers and visitors. Hundreds of people congregate on the steps all day and evening until 1 am. The building provides, for the first time, public space and seating in Times Square, and is the largest trafficable all glass structure in the world. TKTS was the result of an architectural design competition run by the Van Alen Institute in 2007. The project partners were Times Square Alliance, the Theatre Development Fund, the Coalition for Father Duffy and the City of New York. The purpose of the booth is to sell tickets to Broadway shows, and to provide public space in Times Square. The winning entry was a bleacher type form, with a “stairway to heaven` on the roof, and the windows where tickets are sold on the front wall below. The structure is all glass and features laminated glass bearing walls, which carry the roof rafters made from spliced glass fins, and a roof made from glass stair planks. All primary load paths in the structure are glass. Whilst unintuitive, it is quite rational to use glass as a compressive structural element. Glass is practically infinitely strong in compression, and only ever fails in tension. The bearing walls take advantage of this special material property, and carry the entire gravity load of the roof. The walls are simple two inch thick laminated glass with an SGP interlayer. The SGP is stiff, so lends the laminated makeup close to full composite action, and therefore good buckling strength. The base of the glass is grouted to the foundation to form a moment connection, thereby further reducing the buckled length, and improving the buckling and lateral performance of the element. Additionally, pummel testing on the bearing walls showed that direct impact with a sledge hammer will readily break the outer glass ply, but 20 blows are required to break the second and subsequent plies. Any glass structure, no matter how strong, is of course still prone to sudden breakage, so the basic requirement for safety for a publicly trafficable structure drove the requirement for a highly redundant structure. A system of redundancy beams was installed that redistributes load to adjacent panels should any one panel fail completely, or to temporarily carry load should a panel fail. The structure is therefore capable of withstanding an impact from a vehicle, or any number of other accidental or malicious attacks. The glass roof rafters span 30ft between support points. 30ft long single pieces of glass were not available, so a bolted overlap splice configuration was developed. The bolted beam splice connection was not a grouted pin as is more common, but a series of nylatron disks were glued into each ply of glass, which were then drilled through after lamination and assembly of the spliced components. Nylatron is a material similar to nylon, and is drillable with a regular drill. The key reason for this bolting approach was to allow for the even bearing of the bolt on each ply of glass, including allowance for the holes between glass plies to be misaligned. Glass structures are rarely employed because they are the easiest possible way to construct a building, but rather because they serve an artistic purpose. Accordingly, aesthetic considerations were central in the structural design, and the structural design in turn informed the aesthetic design. The canopy that overhangs the front ticket windows is a 2.5 inch thick cantilevered glass element that rests directly on the front glass bearing wall. The canopy is designed for so called Mardi Gras loads, meaning it may be accessed by New Years Eve visitors, and was designed for a full 100psf live load. The cantilever length of 6’-6` makes it one of the longest plain glass cantilevers in the world. Amongst the most challenging details was the connection between the rafters, the front wall, and the canopy. Each element was glass, and was required to draw structural support from another glass element. The glass rafters are relatively slender structural elements that must be restrained against buckling. The stair treads to the roof are structurally siliconed to the rafters using regular Dow Corning 983, and form the lateral braces for the rafters. Buckling is a stiffness related mechanism, so testing was completed to show the long and short term stiffness of the structural silicone.

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